[TowerTalk] C4S and TH6

K7LXC K7LXC@aol.com
Sun, 17 May 1998 19:31:01 EDT


In a message dated 98-05-17 19:19:46 EDT, wa6ibu@earthlink.net writes:

> >      The PEAK gain figures from our tribander comparison test show that 
> the
>  > TH-7 (same antenna/boomlength as TH-6) has 3.3 dBd on 20, 5.7 dBd on 15 
> and
>  > 3.4 dBd on 10M. The C-3 has 4.1 dBd on 20M, 5.7 on 15 and 3.0 on 10M. It
>  > doesn't look like you're giving any performance away.
>  > 
>  Steve,
>  
>  I'm surprised that there is not a larger difference between the two
>  antennas.  The TH6/7 is essentially a 3 element yagi verses the C4 which
>  has only 2 elements per band.  How can the difference be so little.  Is
>  there some other performance factor that was optimized over another that
>  sacrificed forward gain on the TH? 

      Good questions. Remember the TH6 was designed in the 60's in the 'cut-
and-try' age of antenna designing. It took 4 hours per iteration due to making
the change, running the antenna up, running patterns, plotting a Smith chart
and making calculations with a slide rule. The primary design criteria was
maximum front-to-back since that's what the Hy-Gain range does best, not gain.
And it's got traps.

     The C-3 was designed with state-of-the-art computer modelling software
and literally hundreds of iterations before construction began so it's very
optimized. And it doesn't have any traps.

      Don't forget that gain is a function of boomlength, not the number of
elements. The TH7 boom is 24 feet and the C-3 is 18 feet.

Cheers,  Steve  K7LXC

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